1. Field of the Invention
The apparatus of the present invention relates to an offshore platform assembly known as jack-up rigs used for production, exploration drilling for oil or gas, or offshore maintenance. More particularly, the present invention relates to an offshore platform assembly with slant legs, each leg having two vertically spaced bearings in the platform resulting in reduced loading in the legs from the wind and wave forces, the increased resistance to overturning, and the reduced lateral movement of the platform.
2. General Background of the Invention
Most jack-up rig designs use straight i.e. vertical legs. The assembly uses a floatable hull with three or four tubular or latticed legs which may be circular, square or triangular. The legs support the platform in the working condition, and are supported by the platform during transit. Once the legs are located on the sea bed, elevation of the hull to the platform working height is accomplished by elevating units installed at each corner of the platform. These may be rack and pinion systems or hydraulic jacking systems which use friction clamps or pins which engage pin holes spaced at regular intervals up the legs. The jacking system couples the hull to the legs and supports the weight of the hull when elevated.
An example is shown in U.S. Pat. No. 5,092,712. The design disclosed in the '712 patent utilizes an offshore platform assembly which uses inclined legs. The legs pass through a vertical hull and the platform is elevated, flexible leg guides are adapted to move laterally, to some degree, absorbing much of the bending loads and shear forces imposed on the legs, by the use of a compressible member formed as a resilient vertical rectangular sleeve, a spring or other adjustable means which permits a limited lateral bending moment acting on the leg which passes through the guides in the platform hull.